1. Field of the Invention
The present invention relates to a driving device for a vehicle, which is provided with an input member that is connected in a driving manner to an internal combustion engine, an output member that is connected in a driving manner to wheels, a first rotating electrical machine, a second rotating electrical machine, a differential gear unit including at least three rotational elements, and a control device.
2. Description of the Related Art
For example, a technology disclosed in JP-A-2010-76678 may be exemplified as a driving device for a vehicle as described above in the related art. JP-A-2010-76678 discloses a configuration in which the differential gear unit includes a planetary gear mechanism having three rotational elements, the first rotating electrical machine is connected in a driving manner to a sun gear, the input member is connected in a driving manner to a carrier, and the second rotating electrical machine and the output member are connected in a driving manner to a ring gear. In addition, the driving device for a vehicle includes a frictional engagement device that is capable of releasing the connection in a driving manner between the carrier and the input member (internal combustion engine), such that the internal combustion engine is detachable by making the frictional engagement device be in a released state, during executing an electric traveling mode in which a vehicle is made to travel by torque of the second rotating electrical machine in a state in which the internal combustion engine is stopped. Therefore, during executing the electric traveling mode, the rotation speed of the sun gear (the first rotating electrical machine) or the carrier may be set independently from a vehicle speed. As a result, for example, as disclosed in JP-A-2010-76678, the carrier is made to rotate by actively controlling the rotation speed of the first rotating electrical machine, and auxiliary machines may be driven using the rotation of the carrier.
However, in a configuration in which the frictional engagement device is made to be the released state during executing the electric traveling mode like the configuration of JP-A-2010-76678, when it is switched to a split traveling mode in which the traveling is performed by using torque of the internal combustion engine due to an increase in torque required to a vehicle, or the like, it is necessary to switch an engagement state of the frictional engagement device to a direct engagement state, and to increase the rotation speed of the internal combustion engine to a rotation speed at which ignition is possible. In regard to a control at this time, paragraphs 0073 to 0076 of JP-A-2010-76678 discloses a configuration in which the frictional engagement device is switched from the released state to the direct engagement state in a state in which the rotation speed of the first rotating electrical machine is made to decrease until the rotation speed of the carrier is equal to zero that is a rotation speed of the internal combustion engine, and then the rotation speed of the first rotating electrical machine is made to increase until the rotation speed of the internal combustion engine becomes a rotation speed higher than a rotation speed at which ignition is possible. That is, in the configuration disclosed in JP-A-2010-76678, it is necessary that the frictional engagement device is made to engage after the rotation speed of the first rotating electrical machine is made to decrease until it reaches a state indicated by a bold broken line shown in FIG. 9 of JP-A-2010-76678, and then the rotation speed of the first rotating electrical machine is made to increase until it reaches a state indicated by a bold solid line shown in FIG. 9 of JP-A-2010-76678.
However, in the above-described configuration, in a case where an internal combustion engine starting up condition under which the internal combustion engine is started up is established (particularly, when it is determined that the switching from the electric traveling mode to the split traveling mode in JP-A-2010-76678), it is necessary to change the rotation speed of the first rotating electrical machine until the rotation speed of the internal combustion engine reaches a rotation speed at which the ignition is possible, after the frictional engagement device is made to be the direct engagement state. Therefore, there is a concern in that time is necessary to some degree until the internal combustion engine is started up after the starting up condition of the internal combustion engine is established.